There is an old saying about criminals – that they all turn preachers under the gallows. Such is the case with former financier and orchestrator of the largest Ponzi scheme in the history of mankind, Bernard Madoff. In an ironic Christmas Eve letter, he warned about the dangers of Dark Pools – broadly defined as off market volume.

"While I have always been an advocate of electronic trading due to the efficiency the lower costs they bring to the markets, I am [not] a fan of the lack of transparency the DARK POOLS create," said Madoff.

"Institutions have always attempted to guard this buy and sell information from exposure to the market for fear of being FRONT RUN. Certainly they are entitled to have this right of confidentiality. This being said, the more secret this information. The more valuable this information is to those that can obtain it. Therein lies the problem. It is naive to think that there will be no leakage of this information."

This lack of transparency will spread with the recent acquisition of the NYSE, thinks Madoff.

"Although one would be lead to believe that with the recent spate of Insider trading prosecutions, that insider trading is a new development. This is false. It has been present in the market forever, but rarely been prosecuted. The same can be said for front running of orders," concluded Madoff.

Madoff's motivation for writing the letter is unknown. However, it should be noted that before being jailed he made his bones in the stock market, and he was once considered one of the best. On the contrary, Madoff was a thief. He was also very likely a terrible investor. Whatever the case, he clearly is not a fan of dark pools.